1. Field of the Invention
This invention relates to devices, generally referred to as gravity separators, designed to separate immiscible liquids of different specific gravities or densities, such as oil and water, and also to devices designed to separate certain contaminating solid particles from liquids.
2. Description of Related Art
Gravity separators utilize gravity for the separation of the immiscible constituents of a liquid mass, i.e. to separate substances of high density from those of lower density. If the substance is liquid, it is common for the liquid of higher density to be referred to as the "carrier liquid" and the liquid of lower density to be referred to as the "surface liquid." The means of delivery of liquid to a separator utilizing gravity may be in the form of pumped-flow or gravity-flow. In either case, the liquid is disturbed to, a great extent and fine particles of the surface liquid are dispersed in the career liquid. This may be caused in part by the agitation of the liquid by the pump or orifice in the flow to the gravity separator.
Upon entry into gravity separators, large globules of surface liquid float quickly to the surface of the carrier liquid and the surface liquid is discharged through outlets provided, usually above the level of the carrier liquid, or the surface liquid is allowed to accumulate and is skimmed off the surface by suitable means. The size of a gravity separator depends on various factors, for example: flow rate, liquid temperatures, liquid type, presence of solids, difference in the density between the carrier liquid and the surface liquid and also the presence of any chemicals which may affect the gravitational separation of such liquids. Further design features may take into account the rising velocity of a discrete particle of surface liquid, which may be contained within the carrier liquid mass. The rising velocity of a discrete particle is directly dependent upon me difference between the specific gravities of the carrier liquid and the surface liquid, together with the size of the discrete particle, which is usually expressed in microns. Owing to the fact that minute particles dispersed within a carrier liquid rise at low rates, separators usually have to be of enormous size, often making them largely impractical. The reason for this is that the combined residence time of the liquid mass contained within the separator is far less than the time needed for a discrete particle to rise to the surface of the carrier liquid.
Since the rising velocity is largely proportional to the size of the discrete particle, attempts have been made to install within separators various types of plates to coalesce these small particles of the surface liquid into large globules, thereby increasing their rising velocity and insuring that the liquid rises to the surface prior to the discharge of the carrier liquid from the separator. See for example U.S. Pat. No. 4,747,948 to North, and U.S. Pat. No. 4,123,365 to Middelbeek. Such plates increase the surface area upon which coalescing may occur, and reduce the distance which a discrete particle has to rise before being coalesced with other particles contacting a plate. The distance between the plates may vary from a few millimeters to many centimeters.
In many effluent types, however, the size of dispersed surface liquid particles is so small (i.e. the order of 10-20 microns) that their rate of rising can hardly be noticed. These particles are sometimes termed "suspended particles." Effluent may also contain many solid particles which may be rising, suspended, or settling within the carrier liquid, depending upon their density, shape, and size. The separation of such particles is difficult to achieve by ordinary gravity means alone. The use of small bubbles of gas to assist in the separation of small liquid or solid particles is also known in the art. Bubbles attach themselves to the small particles and speed their ascent to the surface of the carrier liquid. Gas bubbles may be generated by electrolytic means. See for example U.S. Pat. No. 3,429,809 to Dotts, and U.S. Pat. No. 3,969,203 to Ramirez. Problems associated with the use of electrolytically formed bubbles in separation equipment include: 1) The distance between the point at which the bubbles are generated within the liquid mass and the surface of the carrier liquid may be too great. Bubbles traveling over this distance may be unable to carry the attached small particles, resulting in shearing of the particles from the bubble, and a reduced level of separation; 2) Even distribution of gas bubbles throughout the separation chamber may not be accomplished due to the electrode arrangement, resulting in incomplete treatment of the liquid to be separated; and 3) Similarly, even distribution of contaminated liquid through the separation chamber may not be accomplished due to channeling or other flow patterns which avoid the area of the separator flooded with bubbles, resulting in portions of the liquid mass not receiving thorough treatment.
It is the object of this invention to overcome certain of the problems associated with the prior art by providing a gravity separator incorporating an electrolytic plate system. It is a further aim of this invention to provide a gravity separator with a flow pattern that requires all of the liquid to be treated to come into contact with the electrolytically produced bubbles. It is yet another object of this invention to provide means for producing bubbles within a gravity separator which evenly distributes the bubbles throughout the path of flow of the liquid to be treated. It is another object of this invention to provide a gravity separator with an electrolytic plate system that minimizes the amount of premature shearing of bubbles from the particles to be separated. It is another object of this invention to provide an electrolytic plate system for use within existing gravity separators.